in full swing 〈口〉正在全力进行中，正起劲;正处于全盛时期，处于兴盛阶段;（聚会、有组织的活动等）正在十分热烈（或活跃）地进行中

【例句】
When we returned, the party was in full swing and the dance floor was crowded.
我们回来时，聚会已进入高潮，舞池里挤满了人。

When we arrived the party was already in full swing.
我们赶到时，聚会已进入高潮。